What % additional fuel is "Full Throttle Enrichment"?

[flightlead404]

The Control Pressure Regulator aka WUR performs a "full throttle enrichment" function based on manifold pressure.

Above a certain manifold pressure the WUR lowers control pressure by 0.5 bar, enriching the mixture.

I'm trying to find out exactly what manifold pressure is the threshold and, more importantly, what % additional fuel is delivered.

If you know the answers or have pointers I'd appreciate it, I've looked everywhere.

[Dmitry at Pelican Parts]

hey flightlead404...I've attached a link to one of our Tech forums that specifically deals with the Fuel Injection system. Hopefully this will help you out a bit. If you have anymore questions, feel free to submit a Comment just below the article and someone will get back to you with the answer. Good luck!

Porsche 911/930 Fuel Injection Tech Article - Porsche 911 CIS Fuel Injection Tuning and Adjustment | 911 (1965-89) - 930 Turbo (1975-89) | Pelican Parts DIY Maintenance Article

-Dmitry

[RarlyL8]

Fuel enrichment via the WUR is a steeply progressive curve that becomes significant at +0.3bar above atmospheric. This is based on the pressure differential at the diaphragm. I have never calculated the % change, only the change in AFR which is dependent on engine modifications.
Why do you want to know % change? It is difficult to calculate (with accuracy) exactly how much fuel is needed for a specifically modified engine to achieve a specific AFR at a specific boost level and RPM. Way too many real world variables. There are 8 different WUR's and 5 different Fuel Distributors mated in the 19 years the 930 engine was in production.

[flightlead404]

According to what I can glean from various docs and tables it comes on at .5 bar and reduces control pressure by a fixed amount (forget, might be .5 bar). However that fixed amount doesn't correspond to a straight % increase across the range. My original question makes no sense because the control pressure reduction translates to increased movement of the air flow meter plate that is non-linear, its controlled not only by the force of the control pressure on the piston in the fuel head, but also the shape of the cone in the air flow meter.

I was just looking to get a good head start on programming full throttle enrichment behavior of the MicroSquirt/FrankenCIS.

[RarlyL8]

I see. If programming you have the option to delay onset of enrichment based on the fuel curve. Once you see the curve as it is you can delay the dump. A Hobbs switch is used for this on standard CIS. I like 0.5bar at the 300-350whp range when using stock boost limit of 0.75bar.
I hope to give F-CIS a go as well once my engine is built and tuned.

[RarlyL8]

Here is a clip of my car that may shed some light:
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[flightlead404]

Originally Posted by RarlyL8

I see. If programming you have the option to delay onset of enrichment based on the fuel curve. Once you see the curve as it is you can delay the dump. A Hobbs switch is used for this on standard CIS. I like 0.5bar at the 300-350whp range when using stock boost limit of 0.75bar.
I hope to give F-CIS a go as well once my engine is built and tuned.

Thanks for the clip. I was really just hoping to build a better initial map to start from when tuning my F-CIS installation.

I have everything for that installation except the block which is somewhere over the Pacific atm.

I'm putting together a detailed step by step for the frankencis and tuner studio adventure which I'll post here.

[RarlyL8]

I can give you static pressure settings I use to tune the adjustable WUR based on your engine build if that will help. This would be cold, warm, and boost pressure. Will need to know which WUR and FD you have along with your system pressure.

[bpu699]

Originally Posted by RarlyL8

Here is a clip of my car that may shed some light:
.

.

Brian, my car does the same as yours, and the AFR goes into the very low 10's or even lower...

I thought that was abnormal??? I thought you shoot for an AFR of 11.5 or so under boost? My car seems to dwell at the low AFR longer than yours does though...

So whats the scoop, normal?

[flightlead404]

Originally Posted by RarlyL8

I can give you static pressure settings I use to tune the adjustable WUR based on your engine build if that will help. This would be cold, warm, and boost pressure. Will need to know which WUR and FD you have along with your system pressure.

Sure that would be a help.

I have a US 1986 930 stock fuel head with lambda and the stock WUR right now. First step is to model that stock setup in FrankenCIS. I have stock headers, K26, B&B muffler, cat delete.

Once I've got this running nicely on a known good setup (car runs beautifully now) I'll change out to your headers and hooligan, K27, tial at 0.8 bar, TK longneck.